check a number is prime or not

// C program to check if a 
// number is prime 
  
#include <stdio.h> 
  
int main() 
{ 
    int n, i, flag = 1; 
  
    // Ask user for input 
    printf("Enter a number: \n"); 
  
    // Store input number in a variable 
    scanf("%d", &n); 
  
    // Iterate from 2 to n/2 
    for (i = 2; i <= sqrt(n); i++) { 
  
        // If n is divisible by any number between 
        // 2 and n/2, it is not prime 
        if (n % i == 0) { 
            flag = 0; 
            break; 
        } 
    } 
  
    if (flag == 1) { 
        printf("%d is a prime number", n); 
    } 
    else { 
        printf("%d is not a prime number", n); 
    } 
  
    return 0; 
}